1. Field of the Invention
The present invention relates to an exchange coupling film and a magnetic sensor having an exchange coupling film, and more particularly, to an exchange coupling film having magnetic anisotropy dispersion and a magnetic sensor having an exchange coupling film with magnetic anisotropy dispersion.
2. Discussion of the Background
Magnetic recording devices such as a Hard Disk Drive (HDD) are required to have a compact external form and high recording density. To achieve these requirements, the recording track width should be narrower for high widthwise density and high recording track lengthwise density.
A MagnetoResistance effect head (MR head) of high sensitivity in reproducing a magnetic signal from a magnetic recording medium of such high track widthwise density has been reported. The conventional MR head had an AnisotropicMagnetoResistance effect element (AMR element) and a Giant MagnetoResistance head (GMR head). That the GMR head can obtain higher sensitivity than the AMR head has also been reported.
The AMR or GMR head each coupled with a planar yoke body was introduced in pending U.S. patent application Ser. No. 08/815,179 which corresponds to Japanese Patent Publication (Kokai) 10-143821.
Referring to FIG. 1, MR film 27 is disposed on magnetic yokes (cores) 24 and also coupled to a pair of electrodes 30. The magnetic yokes 24 are separated by a magnetic gap 25 at an Air Bearing Surface (ABS) which faces the magnetic recording medium. The magnetic yokes are disposed on magnetic shield film 22 formed on a substrate 21. The MR film 27 is separated from the ABS and magnetic gap 25 at ABS is so thin that the required high track widthwise and lengthwise density is obtained by the head structure. A magnetic signal from the medium is picked up by the pole tip portions of the yokes separated by the gap 25 at the ABS and introduced to the MR film 27. A resistance variation of the MR film 27 is sensed by a voltage detector coupled to the pair of electrodes 30(not shown).
Magnetic domain walls 36 each surrounding a large magnetic domain of magnification direction transfer in the conventional magnetic yoke 24 as shown in FIG. 2 and the movement of the domain walls 36 produces an irreversible change in magnetization direction that the signal transmission in the core 24 may be discontinuous enough to raise the BaukHausen Noise (BHN). Such magnetic domain wall movement causing magnetic transfer in the conventional magnetic yoke 24 has a large influence because area of the yoke is up to 200 micrometer.times.200 micrometer and discontinuous signal transmission becomes a larger problem to magnetic variation than the one in a magnetic body having an area of 1 centimeter.times.1 centimeter.
FIG. 3 is data showing relation between external magnetic field (H) and magnetization (M) of the conventional magnetic core 24 recently obtained by the present invention (Delta Mb)/delta M) in every directions of the conventional magnetic core, which is around 30%, as shown in FIG. 3. Where delta Mb is most drastic magnetization change which appears as BHN and equal to difference between the MB1 and Mb2. Delta M is the magnetization range of the exchange coupling film ranging from negative saturation magnetization (minus M) to positive saturation magnetization (plus M), when external magnetic fields (H) are applied to the exchange coupling film. The M-H curve may be measured by a well known magnetization using the Kerr Effect. The M-H curve shows some drastic changes and most drastic change in the M-H curve is change at outer magnetic filed H1 changing Mb1 to Mb2 like step.